Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $162.63   11.262%   $180.9454   $180.95   $180.95   $180.90  
  Purchase #2 $228.31   13.510%   $259.1547   $259.15   $259.15   $259.20  
  Purchase #3 $227.40   10.462%   $251.1906   $251.19   $251.20   $251.20  
  Purchase #4 $64.59   4.426%   $67.4488   $67.45   $67.45   $67.40  
  Purchase #5 $14.86   4.166%   $15.4791   $15.48   $15.50   $15.50  
  Purchase #6 $203.55   11.311%   $226.5735   $226.57   $226.55   $226.60  
  Purchase #7 $104.27   9.112%   $113.7711   $113.77   $113.75   $113.80  
  7 purchase totals = $1,005.61       $1,114.5632   $1,114.56   $1,114.55   $1,114.60